I think that the idea that your team came up with was solid, but as you mentioned the execution and follow through fell off a bit after the semester ended. I would recommend in future, ensuring that all team members have something that they can work on. It doesn't have to be in Unity specifically, it could be iterating on materials and models or testing mechanic and system loops in a separate Unity project or researching how to implement certain features, etc. Having your project management setup, even if it is basic, should help with this in future.
Also, I'm not sure if you guys implemented occlusion culling for this, but if the map is still one massive mesh instead of the modular setup I suggested, then it might be worth looking into this over the summer as it is a fundemental technique that will be a great addition to your arsenal in September when you start working on 3D games. Feel free to keep the Github action I helped you setup, that will also be useful in September.
Good luck to all of you next year, it's been fun